CYTOGENETIC CHARACTERIZATION OF TWO SPECIES OF Hypostomus (SILURIFORMES, LORICARIIDAE) FROM TRIBUTARIES OF THE VERMELHO RIVER, UPPER PARAGUAY RIVER BASIN

2* ABSTRACT - Cytogenetic data are presented for two fish species of the genus Hypostomus from two streams belonging to the upper Paraguay river basin in the state of Mato Grosso, Brazil. There are no reports in the literature on the cytogenetic features of Hypostomus species from these localities. Hypostomus aff. cochliodon presented a diploid number of 2n=64 chromosomes (18M+20SM+26ST/A) and Hypostomus sp. showed 2n=74 (12M+20SM+42ST/A) chromosomes. Multiple nucleolar organizer regions were evidenced by silver nitrate staining in analyzed species. Hypostomus aff. cochliodon exhibited large heterochromatin segments at the terminal regions of three chromosome pairs. These results confirm previous data concerning the Hypostomus genus and reinforce the importance of studying the ichthyofauna of Mato Grosso, providing perspectives for future research in the area of cytogenetic and molecular biology to elucidate unresolved issues of evolution and taxonomy.